Over the last few years, the demand for high-speed communication networks has increased dramatically. In many situations, communication networks are implemented with electrical interconnections. As desired levels of bandwidth and transmission speed for communication networks increase, it will become more and more difficult for electrical interconnections to satisfy these levels.
One difficulty associated with electrical interconnections is that they are sensitive to external electromagnetic interference. More specifically, electromagnetic fields that reside in the vicinity of the interconnection lines induce additional currents, which may cause erroneous signaling. This requires proper shielding, which hampered general heat removal.
Another difficulty is that electrical interconnections are subject to excessive inductive coupling, which is referred to as “crosstalk”. To alleviate crosstalk, the electrical interconnections must abide by fundamental rules of circuit routing so that they are set at a distance large enough to prevent neighboring signals from having any adverse effect on each other, which would reduce network performance.
In lieu of electrical, optical interconnections offer a solution: to the difficulties affecting conventional electrical interconnections. For example, optical interconnections are not as susceptible to inductive or even capacitive coupling effects as electrical interconnections. In addition, optical interconnections offer increased bandwidth and substantial avoidance of electromagnetic interference. This potential advantage of optics becomes more important as the transmission rates increase and as the strength of mutual coupling associated with electrical interconnections is proportional to the frequency of the signals propagating over these interconnections.
Albeit local or global in nature, many communications network features electronic switching devices to arbitrate the flow of information over the optical interconnections. Conventional electronic switching devices for optical signals are designed to include a hybrid optical-electrical semiconductor circuit employing photo detectors, electrical switches, optical modulator or lasers. The incoming optical signals are converted to electrical signals, which are amplified and switched for driving the lasers. One disadvantage associated with a conventional electronic switching device is that it provides less than optimal effectiveness in supporting high data transmission rates and bandwidth.
An alternative approach is to develop all optical, scalable cross-connect system, which performs switching operations of light pulses or photons without converting and reconverting signals between the optical domain to the electrical domain. As described below, the subject invention provides an optical, scalable cross-connect system with a variety of features such as redundancy for fault protection and non-intrusive, dedicated test access ports for example.
An important problem faced by network operators is how to reliably connect (i.e. link) various types of network equipment with all-optical equipment such as an all-optical cross connect switch. It is desirable to provide adequate protection so that in the event of a connection failure, service is not lost or substantially interrupted. Protection mechanisms can be employed within the all-optical equipment to increase their inherent reliability. Other protection mechanisms can be employed to increase the reliability of the overall communication system. However, just as important is the optical connections between the network equipment and the all-optical equipment. It is desirable to provide a protection mechanism for the optical connections between the network equipment and the all-optical equipment that differs from the system and the equipment protection mechanisms.
A connection failure can occur in a single link between the connection of the various network equipment and the all-optical network equipment. This may be the case for example if a fiber optic cable is cut or damaged or if a fiber optic cable is unplugged from a port of either the various network equipment and the all-optical equipment. Alternatively, a connection failure can occur in the various network equipment or the all-optical network equipment itself due to a failure in a port of either. This may be the case for example if a component in a port card fails and does not allow a signal to propagate through the all-optical equipment. An exemplary component that might fail in the port card of the various network equipment would be an electrical-to-optical converter or transmitter.